I dont think WiiGuide would be a Trademark Issue, if your site is as the title suggests is a 'Guide' to the games on Nintendo Wii. Such a site only serves to promote Nintendo and the Wii Console.
The Term 'Guide' is also a generic word which cannot be trademarked.
Could you imagine if Microsoft decided to shutdown every site that uses the term 'xbox', they would basically be throwing billions of dollars away in sales and free promotion.
However it can become an issue if you decided to build site defaming the Nintendo Wii.